On Sat, May 8, 2021 at 5:29 AM Jia He [off-list ref] wrote:

This helper is similar to d_path except for not taking seqlock/spinlock.

I see why you did it that way, but conditional locking is something we
really really try to avoid in the kernel.

It basically makes a lot of static tools unable to follow the locking
rules, and it makes it hard for people to se what's going on too.

So instead of passing a "bool need_lock" thing down, the way to do
these things is generally to extract the code inside the locked region
into a helper function of its own, and then you have

  __unlocked_version(...)
  {
       .. do the actual work
  }

  locked_version(..)
  {
      take_lock(..)
      retval = __unlocked_version(..);
      release_lock(..);
      return retval;
  }

this prepend_path() case is a bit more complicated because there's two
layers of locking, but I think the pattern should still work fine.

In fact, I think it would clean up prepend_path() and make it more
legible to have the two layers of mount_lock / rename_lock be done in
callers with the restarting being done as a loop in the caller rather
than as "goto restart_*".

              Linus